Cladding metal



Patented May 26, 1953 T. fllaytomfih-ltimore, Md assignnr to The Tainton Gompaam, Baltimore, Mid a corporation oftMai-ylaml No Drawing. Application April 17, 1951,

SefialNo. 221,535

J52 Claims. (Cl. 117-409;)

invention relates to the art of metal plataml is a continnati'on'inpart form U. S. va1)- plioa tions No. 3;537 filed January 271, race, 21%. H5639 filed March ll-2, 1948, No. 77,7369 filed Februa-ry i8, 19% and N0. $9,567 illed June 516, i949 (Nos. 539 and 77,269 having heen abandonedi). Specifically it relates to the art of isufi-acing :one metal with another in which 'a metallic coating built up of sma l] particles of the coating metal depos'ltel the hase surface and overlaid with similar fiepcsits of Fpa-rticiles 'interiitted in meta-1 to 'metal contact whereby a dense metal coating is incrementally built up, without the employment of'either externally applied melting heater elecwavy.

object of the invention *is to provide a metallic coating which is efiective'ly adherent to the base; inexpensive in application, attractive in appearance, and 'oroteetive against weather.

'iiszrot'her ob'il'ect is to proviso means whereby metals "liihoult or impossible to plate lay more conventional "methods, may be successfully plated on rail of metal surfaces mcluding such 1 efractory "and rliificul t surfaces as magnesium. The use-o1" this methol permits multiple or layer coats oi fiifferent metals to be wlepos'ited on the surfaces of objects.

The invention thus :relates to a method 'mecharfically plating aluminum, copper, cadmium, tin, lead, titanium, 'gdlil, silver, alloys or mixtures thereof anti stainless anil other steel alloys or mixtures thereof and other metals on smiaces, articles 'and objects.

A further :purpose of this invention is to prov'ide a simple meansior applyin 'alloy coatings. Basically this invention utilizes the application of mechanical ,forces to very small particles of metal. These forces are sufficient to suddenly anllfiras'tically distort each metalparticle'beyond its elastic limits. The metalparti'cles used in the operation may be particles of a metal fiust made lay condensation from a vapor phase or by air-disintegration of .the moltenimetal, .or by other means. In every case, however, natural laws operate "to protluce particles having ahiin'irnum surface area. Thus, the metal particles "are round cr;pear shaped, andthe majorpart of th'eir mass is in "the interior. When such a particle havinga minimum surface areais "acted upon by forces sufllcient .to suddenly, "tlrastically distort and flatten "it, its surface area is "'greatlyincreased, anti metal "previously contained on the inside OT each particle becomes a part of the surface. such a particle "is *fl'atteneii in contact with -or against a similar particle, and cleanunetal-surface is brought into mtimate contact with clean metal of the adjacent particles which has'also lbeen xlis touted, then seizing 01 welding: of the clean surfaces in metal to :metal contact with each other ensues. Locally generated heat at the moment of impact is theoretically "very large and assists in the promotion of the welc'lor fusion of thetwo particles.

In the huilduqo'of metallic :coatings using this method, two cases :arise. The first is the :adhesiye bondtoriieposition oi the initial-or covering lay-er of nazlticles onto metal :base, and the second is :the cohesive hand our deposition of subsequent layers of particles onto thosepmeviously-deposited. In the first case the surface to .be coated is :usually a hard massive fsimface, frequently of steel or other equally ihard :metal. Forces sufiicien-t to drastically iiistnrzt and .fflatten a very small particle may he relatively ineffective producing any appreciaiole distortion of the massive abase. Hence, only one member "in the mating of these surfaces is distorted and consequently to increase the adherence the .smfface to be coated :is slightly etched to present an irregular surface full of microscopic cracks and .pnotuberences so that :the coating metal maybe plastically deformed by the applied forces into and around these surface tirregularities; ithe clean metal :surfaces exposed iby the etching and by the deformation of :the :coating particles uniting to iorm a strong .adhesiye bond. The surface roughnessof the metal base may 'be achieve'd by acid pickling, grit blasting, abrasive tumbling "or :other means calculated to provide -either a microscopically 'or macroscopically rough, chemically clean, active =surface.

The application of forces suffi'ciently great to suddenly'and drastically distort apartiole when in contact with the base, upsets the mormail atomic arrangement and imparts a very high energy "level to the particle whereby atomic mobility is greatly increased, anti diffusion of the atoms of the 'two surfaces joined in this way one into the other-occurs and an atomic bond is created. It -w-ill be apparent that under the right conditions on infinitely thin metal coating may be rubhed or rsmeared "into the sur faoe cracks and irregularities of another metal to provile an influitely'tliinooating. Such co'atmgs are usually completely adherent, but are so thin that ithey provide little or no =pro'tection against corrosion, or, *at best, they are suitable only for "indoor or temporary use. Smear-ooatings laid downin this manner, while not-commomare not newJbut ane olil in ar t. 'fl heyare usually achieved dry tumbling in sham-"e1, Pout could equally wellmnder certain conditions, be laid down using a wet technique,

It is clear that a multiplicity of impacts on the 7 base article suflicient to distort metal particles in contact with its, must exert a substantial scrubbin-g abrading force tending to tear off protuberances and to smooth and polish the article. For example, if the article to be plated is agitated in a ball mill with a hard abrasive substance, such as crushed iron shot, and a metal dust, and a liquid, the effect of the tumbling action would be to grind the metal dust and to polish or :burnish and smooth the surface of the article. This would be especially true if the metal dust had filled in all surface irregularities of the base which would then present a perfectly smooth surface. That this does in fact occur is well known and'tumbling barrels have been used for many years for burnishing, deburring and polishing. This burnishing is done both wet and dry and various soaps, wetting agents, and other deter gents are used to assist the tumbling action to achieve a higher polish or greater smoothness.

Thus, the provision of impacts necessary to distort the metal particles carries with it a burnishing or deplating action which, in the past, has served to bar any further progress in the field of mechanically applied coatings other than may be achieved by the smeared type, just discussed, which is deposited into surface irregularities of the base. I have discovered thatthe character of the rubbing, abrading or impacting force must be modified as a necessary preliminary to the build up of thick cohesive coatings in admixture with liquids. This modification may best be secured in a most surprising and unexpected manner, namely, by filming the surfaces of the articles, the metal dust and the impacting medium with a molecularly thin film of certain gummy, oily or fatty substances. It is rather extraordinary that plating in admixture with liquids can best be promoted by the use of what would appear to be the substance most likely to prevent plating. The whole art and science of lubrication is based on the'necessity of keeping mating metal surfaces apart by interposing a film of lubricant. On the other hand, in the complete absence of all films the ability of clean metal surfaces brought into intimate contact to seize or weld is well known. It applies in greater or less degree to all metal surfaces and to many other types of surfaces as well. A familiar example of this is the seizing of an automotive engine when lubrication fails.

Films of one sort or another are invariably present on surfaces. In the case of metals, the films may be composed of decomposition products of the metal, such as oxides, carbonates, sulphates, etc. Metals in common with other surfaces in air or liquid are encased in a thin, gaseous or liquid lamellar viscous envelope. To illustrate, the heat losses incurred in passing heat across a metal surface are known to occur for the most part in this envelope and not in the metal itself.

For the build up of metallic coatings through the incremental sintering into place of small particles, I find these naturally occurring films that exist on the surfaces of the metal dust particles used in the process are objectionable and interfere with plating and must be removed. While it is true that the action of the mechanical forces used to distort the particles may serve to scour and clean the surface of the particles, in an ordinary liquid or gaseous environment, such films constantly reform.

I find, as has been stated above, that the most satisfactory way of removing undesirable films and ensuring that they stay removed, is to use a film former which displaces unwanted films and replaces them with films of a suitable kind which may later be parted or squeezed out from between mating particles in the coating. The film former reagent used to allow plating must therefore have very strong film forming properties of its own to enable it to displace other tightly, adherent films. It should preferably have a solvent action on metal oxides, and it should be present on the metal particles in the form of a very thin, more or less, mono-molecular layer so that it may be easily parted by applied distortive forces. It is best present in a sufficiently thin layer so as not to film over new metal surfaces created by the increase in surface area of the particlegas discussed previously.

In general, these film forming materials consist of organic surface active agents having polar molecules. Specifically those materials having both a hydrophilic or water accepting group, and.

a hydrophobic or water rejecting group in the.

molecule, are especially suitable. The hydrophobic end attaches itself to the metal surfaces in the plating bath which are thereby completely filmed. Non-ionic or cationic substances are more effective in promoting plating than do the anionics. Non-ionic materials have the further advantage that they may be used inconj-unction with either cationic or anionic materials and they are usually sufficiently stable that they may be used in either acidic or basic media. ability of cationic oil emulsions to completely ex-. haust themselves onto the surfaces of metals in' liquids has been established. This property aids in keeping the quantity of plating promoter at a minimum. Besides being goo-d film formers, the ideal plating promoters should be good wetting agents; they should be good detergents to assist the tumbling action in removing unwanted oxide or other films.

Preferably, the plating catalysts should be poor electrolytes, as the presence of ionisable inorganic salts at the metallic inter-faces of different metals, such as zinc and iron sets up galvanic side effects. Inclusions of this sort, that are retained in the coating, serve as foci of attack,

with resultant corrosion, especially Where the fiuxing material exhibits any hygroscopic quali ties.

Preferably, the plating catalysts should be,

beneficial when retained in the coating in they form of minute occlusions. Thus, they may be corrosion inhibiting and tarnish resistingl There are a great number of materials available that exhibit these properties in greater or lesser de-" gree. I find that different plating promoters pro-' foundly affect the adhesive and cohesive bond, the

rate of plating, the thickness of. coat achievable;

attach-a the vlortshtness and or the deposit and, that this is especially true when the plating promoter is dissolved or dispersed water.

1 do not wish to be limited to any theory as to why diiierent plating promoters should have such a vital enact on adhesion, rate hf plating, etc, but it is probably a function of minute inciusions retained the coating, the effective ness of the detergent action, the strength, tides? ness and character of the lllm the metal surlaces, and the viscosity of the solution. Since there are many types of formers "that will allow plating to occur under proper mechanical conditions, a selection or one so eive the best adhesion, most rapid plating, etc, has required a'tremendous amount or esperiinentatien.

l rind that the l atty acids, as a class, are especially suitable. All or the fatty acids, when dis solved or dispersed in a sulta'hle carrier, are eiiective either alone or in combination with other him formers, For example, the acid can be derived from fats or tallow, vegetable, marine or organic oils, as for instance, linoleic acid, linolenic acid, eleic acid, eluponadonic acid, the fatty acids derived from rapeseed, linseed, flax seed, palm, and scya beans. in general, any of the cheat urated monobasic fatty acids of the series finfizn fiGz ma be utilized. 0f the fatty acids the low molecular weight saturated acids, such as caproic, eidective, 'but the long chain unsaturated acids, such "as oleic, linoleic or ricinoleic are extremely good. When used in water, the fatty acids recuire an emulsifying or "solubilizing agent as will be described later. A great many compounds derived "from fatty acids, such as products of the reaction of fatty acids with ammonia; such as fatty acid amides, fatty acid amines, are part'i'cularly suitable for promoting plating as are the fatty acid salts, such as the acetates. Where water is used to carry and dissolve the plating promoter, the various gumsysuch as sodium, ear'hoxy methyl cellulose, and the natural gums, such as acacia, "are very effective particularly when used in conjunction with an organic carooxylic acid or ammonia. Still other types or organic acids may be used. such acids, for ex"- ample, may he tartaric acid or oxalic acid or one of the amino acids such as glycine. I have also found that the metal soaps such as zinc linoleate or mine oleate may function as better plating agents.

In as much as these organic films are usually of the order of one or more molecules in thickness, the film former or plating promoter may be used very small quantities despite the enormous surface area of the metal dust to be coated. This means that these film formers or plating catalysts, or promoters, must be dissolved or suspended, or otherwise carried in some other liquid which thus serves as a carrier or Suspender liquid, the principal function of which is to distribute the film formers or catalysts over the metal surfaces.

The carrier liquid in which the organic surface active fil" former is carried may be any liquid oi suitable viscosity and. physical characteristics, inert to the plating promoter, capable of dissolving or otherwise dispersing the surface active agent. For example, the carrier liquid may be any of the group consisting of water, hydrocarbon solvents, aromatic solvents, coal tar derivatives such as xylol, naphtha, mineral spirits, toluol, alcohols, ketones, esters, ethers, organic phosphates, organic oils, many plasticisers, etc,

capryl ic and capric are particularly 6. etc. The carrier liquid selected to carry the plating promoter or catalyst determines the category or division in which plating occurs. These divisons are the aqueous system and the non-aqueous system.

Dealing first with the aqueous system. and con electing a practical application of the inven tion, the plating may be done by tumbling in a ball mill. The articles to he plated which may, fer example, be nails, lirads, screws, belts, nuts, small haidware, poleline hardware, small stampings, rioreihgs or machine parts, are given a suitable cleanilig treatment such as an acid pickle. They are well washed and added, while still wet, to the hall inill, tumbling panel, or other agitatin device. impacting material used ,7

for hammering or impacting the coating onto the articles may be crushed iron shot, small halls, shot, nail clippings, coarse metal dust, or, the case of syn-all articles like tacks, they may serve as their own im acting material. A very satis factory mixture is five arts, by weight, of new dered metal to four parts, by weight, oi liiiuiil. '1 have round, however, that range can vary from seven parts powdered metal to one part li uid and ohe'part powdered metal to tour liquid and still produce satisfactory results.

This hard material is added to the mill th eether with fine metal dust which will serve as a raw material from which the heating is b'nilt up. The plating chemicals are then dissolved, dispersed or suitably emulsified in water, and liquid is added to the mill. The mill is closed and rotated and a substantial adherent coating will be built up on the surfaces or the articles. The plating promoters used with water are ex tremely important. The water functions only as a carrier liquid to disperse and distribute the active promoters 'over the metal surfaces. Water by itself is harmful. For example, agitation of very fine aluminum dust or very fine zine dust in plain water in a sealed mill leads to the produc- 'tion of substantial pressures through hydrogen evolution caused by reduction of the water. Moreover, there is nothing present in plain water by itself to assist in the chemical cleansing or metal surfaces. Any eiiect is exerted indirectly the opposite direction; the water sup lying oxygen under ideal oxidative conditions. Water alone is thus typical of carrier llquiels it adds nothing to the promotion of plating, but may be detrimental. The action of the film former filming the metal surfaces serves to insulate them from the water and no attack by the water on the metal occurs. With a suitable selection of platlng' promoters it is possible to o erate closed and hermetically sealed mills using water and such reactive metals as magnesium, but gas is generated: but rather a vacuum is created.

The magnitude of the distortive forces applied to the metal dust particles may he regulated by the type and quantity of hard impacting material used, the quantity of cushioning fine metal dustused, and by the size of the mill which in tuln requires regulation of the amount of free space or free fall of the charge, and by the colleentration and type of him former used as well as by the viscosity and physical characteristics of the carrier liquidin this case water. The adjustment of these variable can readily be illustrated by examples which will follow, and which show the wide limits po sible in the mechanical pro portioning orthe charges.

By proper balance or the different factors invo'lved, a viscous solution heavily loaded with 'fihe metal dust may counteract the effect of a mill loading which might otherwise be too abrasive in its action. Similarly, very powerful and rapid plating promoters may function well in a mechanical loading which would be unsatisfactory if poor plating promoters were used. The examples again will serve to illustrate the adaptability and tolerances possible in the practical application of the process.

In the non-aqueous system of plating, in which the carrier liquid is something other than water, a number of major and very important changes may be made. To illustrate, the excellent solubility of the fatty acids and many of their important derivatives in solvents, such as alcohol, hydrocarbons, coal tars, etc., makes it possible to eliminate couplers, emulsifiers, or other agents usually necessary when using fatty acids in water.

A non-aqueous system may be operated at temperatures substantially below the freezing point. In the plating of certain articles the use of water is sometimes inadvisable, especially where every trace of water must subsequently be removed. For example, the insides of metal propeller blades for aircraft. The use of non-aqueous systems is occasionally of value where complete and rapid drying is required. The high solubility and inert characteristics of many non-aqueous systems lend themselves to the use of simpler types of film formers and to continuous operation. The highly reactive nature of water, when in contact with fine metal powders, is not as suitable for continuous cyclical operation of the process as nonaqueous liquids where the plating efiiciency of water may fall off rapidly after a number of recycles, due to the accumulation of hydroxides and other decomposition products; non-aqueous baths can be kept in operation for prolonged or indefinite periods of time by the adoption of proper physical and temperature conditions, and the selection of suitable plating promoters. In such continuous operation, fresh metal dust and fresh plating promoters must be added to replace losses due to dragout, and plated on the articles. Under proper conditions it is possible to plate batch after batch of articles using the same liquids.

I have found that whereas a fatty acid, such as caprylic, in a solvent, such as mineral spirits, may become inoperative if continued in use for prolonged periods, the same mixture will continue to plate if the temperature is raised to approximately 165 F. Articles plated under such conditions have a remarkable luster when removed from the mill, and are astonishingly tarnish resistant; so much so that pieces plated under the above conditions have retained almost all of their original luster for periods exceeding one year when stored in open containers in air. This luster retention and tarnish resistance appears to be especially pronounced in the case of non-aqueous plating, and is apparently due to the retention of minute amounts of fatty acid in the coating.

Organic alkalis, such as the fatty acid amines, have been found to be particularly useful in continuous cyclical operation of the process where batch after batch of articles are processed, using the same liquid. Of these organic fatty amines, I find the tertiary amine of a long chain fatty acid to be particularly effective. For example, if R represents the carbon chain corresponding to the fatty acid, then the primary amine is RNI-Iz in which one of the hydrogen ions of the ammonia has been replaced with an alkyl radical. Where two or three of the hydrogen ions are replaced,

the amine becomes a secondary or tertiary. amine respectively.

A preferred primary amine is one derived from a soya base and has the following approximate composition: hexadecyl, 10 per cent; octadecyl, 10 per cent; octadecenyl, 35per cent and octa-s decadienyl, 45 per cent. A tertiary amine derived from this primary amine is obtained by condensing ethyline oxide with the primary amine.

Since the amines are alkaline, they may be reacted with other fatty acids or with organic or inorganic acids to produce neutral salts. For example, the amine acetate formed by reacting the amine with acetic acid, has the desired characteristics for plating.

The amines are another type of aliphatic carboxylic derivative which produce satisfactory results. The primary amide as used in my method is defined as the derivative of an organic acid in which an amino group replaces the OH group; Therefore, using R as before, a primary amide is The secondary and tertiary amides are par: ticularly useful in both aqueous and non-aque0us plating baths. The tertiary amide which is a N-substituted fatty acid amide; the substituents being polyoxyethylene groups, is especially desirable, particularly when highly substituted, It is a water soluble, chemically neutral, rather unreactive, film forming, oily material that is especially desirable. in combination with fatty acids. In water it functions as a solubilizer or coupler for the acid. These tertiary amides and-amines are particularly effective in non-aqueous liquids for continuous cyclical plating in which the bath is kept in operation for weeks at a time by the addition of fresh metal dust and infrequent renewals of plating promoter. The tertiary amides and amines when used in combination with organic carboxylic acids or fatty acids are also especially effective in aqueous systems, as has already been mentioned.

The properties of clean surfaces which enable one clean surface to weld or fuse to another are not limited to any one group of metals, or indeed to metals. A chemically clean and optically fiat glass plate may be made to adhere strongly to a similar glass merely by pressing them together. Highly polished metal blocks may be made to adhere to one another. A clean glass surface may be bonded to a clean metal surface. Measure ments of the force required to pull such surfaces apart runs, in many cases, to many tons per square inch. In powder metallurgy, different metal powders may be compressed at room temperature or at temperatures far below their. melting points, and bonded together to form compacts.

In view of the above, the application of the principles set out previously to all metal powders makes it possible to plate any metal.

In practice, metals such as zinc, cadmium, tin, lead and light aluminum coatings may be so plated.

Metals such as zinc, cadmium, tin and lead are readily built up into substantial coatings, while metals such as copper, silver, stainless steel, etc., etc., under similar circumstances, could. at room temperature be applied only as a thin smeared on type of coating. I have found that these differences in behavior are tiedin with the minimum recrystallization temperatures of the metals when in the drastically Worked condition.

Consider the operation of a tumbling barrel or ball mill for the moment in which finely divided assume metal powders are acted upon. by small metal;

shot in the presence. of a suitable: liquid and. the

obrlbcts which are to ice-plated- Mechanical: work done in a mill operating under these conditions; is sufficient to. raise the internal temperature. of; the mill several degreea and the local; temperature atthe point of impactbetween metal objects and shot may be substantially above. temperature. In view of this phenomenon; in: the. plat..- ing of zinc the temperature involved may be well above room temperature. In the case of drastiworked aluminum, this: temperature may be reached in local. areas: at. the point. of impact... 'Ehus, the plating: of metals, such. as. zinm, lead='.. cadmium and tin, may proceed well above. their minimum recrystallization. temperatures: without. the application of externally app-lied heat... which. has: a higher recrystallization temperature (probably about d C.) falls imam intermediatezone. Light coating-s of aluminum: tot .0003 may be achieved; in media.v witi'lout the necessity for applying heat; @ther rrretalsv hating higher recrystallization temperaturescmnst be raised in temperature so; that. platthe is done; above the, minimum recrystallization temperature; for the metal. being plated.

Operation at temperatures-well?above the mum recrystallization temperature frequently results in improved results and faster plating. @peration at. above room temperatures are more suited. to nomaqueousbaths. than. to water con taming mixtures.

the: plating of zinc in mills run. at L59 it has been toundi possible to apply light coat-- ings unthout zinc dust: being introduced, the zinc: for the reaction coming; train. the. zinccoatcda shotused. and the zinc lining: which builds: up: on the inner surfaces of; the. mill. Plating. without zinc: dust. in this way results the application'of light coatings which are characterized by: extreme smoothness and a very high degree of luster. A. verysuitable fatty acidfor plating; without zinc dust is caprylic acid. Analysis of the plating liquid discloses that a substantial quantity cfzinc dissolves as a metal soap and it is poss blethat" some of the zinc the coating may be derived from a solution phase.

Where externally applied heat is used, as for example in the plating; lot-chipper or silver where both have minimum recrystallization temperawas of 2 60 C5,, it is necessary to use different carrier liquids and sometimes different plating agents. The, carrier liquids described above do not have boiling points sufficiently highfor use at 200 but other liquids, suchas butyl' stearateor tri-butyl phosphate are quite suitable. Other suitable liquids may be found in the light oils, such as whale is sold commercially under the trade-name of Cosmol. For temperatures ot1200 C., and higher, it is also possible to use materials which may be soli'dat room. temperatures, but; which are quite fluid. at. the operating temperature of the plating bath. Materials of character are solid al'oohols. such as the sterol' alcohols, and some of the fats. A. commercial product known as tin fat. which is. used in place of palm oil in the hotdi'pping of tin plates is. also suitable as. a carrier liquid for elevated temperature plating using, this. method. Several oi. the fatty acids are suitable m. use. at. elevated temperatures. which is. less. desirable. for work. at. room. temperature, workswell at elevated temperatures... Oleic acid is also, well. adapted for use at. higher oil, a purified version or" which Stearic acid,

temperature. Neutral fiused salts are available as liquids for the plating; of." metals higher recrystallization temperatures. than copper and silver. Plating under pressure extends the range of some liquids. Howeverthe coating is derived, mechanical. agitation. attrition. or impactis present in all cases and is an essential. part. of the process.

I do not wish to be limited to any particular theory involving recrystallization oithe grains,

but I findthat the-recrystallization temperatures provide an exact guide as to the temperature re-- quired. The recrystallization temperatures may be the minimum given for any particular metal 1 which has-been drastically worked. It should be noted that in the practice of this invention conditions for the drastic working of the metalbeing applied are present. It is understood. that recrystallization may occur over awide range oi: temperature, starting, for example, withtin and lead which begin to recrystallize at room temperature, aluminum which begins to recrystallize at C., and copper and silver which begin. to recrystallize at. 200 (1., up through. the. lowestrecrystallization temperature. of other metals and alloys. Taking. a. specific example, such as. zinc, it will be noted that. it recrystallizes] at room temperature. Room temperature is. a variable quantity. Successful zinc plating as has been stated may be achieved when the temperature is raised substantially above .roomtempetature, but if the mill is. cooled sufficiently for be.- low room temperature, then no plating of zinc occurs. This is, therefore, exactly ana1ogous..to. the case of. copper which. at. room temperature is. sufficiently below its recrystallization tempera.- ture that no plating occurs. Some alloys recrystallizeat. room. temperatureor below. and. many,- alloys have been plated at room temperature... This alloy plating. includes bothsolid solution and two-phase alloys. For.- exa-mple, it is pose sible, using the methods. of this invention, to. take copper powder and; zinc. powder and to run them together in. the mill: with the. proper: liq-- uids and the proper charge of shot SQithEl-it yellow alpha brass is formed from these two difierent metal. constituents. This yellow alpha. brass appears as a bright adherent coating. on. the. metal objects. placed in the. mill. for plating. Qthm: solid solutions have. also beenplated in a simi-. lar way at room temperature.,

Plating at. temperatures that. fall near the minimum recrystallization. temperature is. done: at: heats: far removed from the melting point of the'metal being, plated: Copper, for instance, has:

a minimum recrystallization temperature of. about: 200: C- Themeltingi point ofcopper is 1083 C., so that plating; may be accomplished at: a temperature over 809 C... removed from the melting point. Other metals having higher recrystallization temperatures, such as iron (about 400 CL) have still higher melting points so that substantially the same temperature di'fierentiai between plating temperature and} melting point exists.

When plating at minimum recrystallization temperatures, no detectable diffusion ofthe plating' metal into the base occurs. It is recognized that when plating with low melting point metals, it is possible that if the temperaures are raised high enough, some dififusion' might result.

Zinc is an example of a metal that will diffuse into the base layer if the temperature is sufficiently high.

The following examples will serve to illustrate the practice of the invention:

EXAMPLES Example 1 Metal dust to be plated (e. g. zinc) lb 7 Nails lb Solvent (V. M. 8: P. Naphtha) qt 2 Lubricant (oleic acid) oz 4 Example 2 When plating screws the following is satisfactory:

' Three pounds zinc dust, twelve pounds of metal shot No. 1110, two quarts of high-flush naphtha and 100 cc. caprylic acid were added to a five quart porcelain laboratory jar, together with an assortment of washers and other small hardware which had been well pickled in acid and subsequently washed in boiling water. The jar and contents were then cooled with carbon dioxide to a temperature below minus 20 C. The

mill after cooling was revolved for twelve hours in an insulated cabinet which was cooled by 150 pounds of solid carbon dioxide. At the expiration of this time the mill was opened and the objects therein were found to have no zinc plating on them.

1 Example 5 A five quart laboratory jar was charged in exactly the same manner as that outlined in Example 4 above, and was rotated for twelve hours at room temperature. On opening the mill the objects were found to be coated with a bright lustrous dense coat of zinc metal which was four thousandths of an inch thick (.004").

In Example 1 listed above, the zinc was below its recrystallization temperature and no plating occurred. In the fifth example, it was well within its recrystallization temperature range and heavy plating was obtained.

Example 6 Three pounds of copper powder, together with twelve pounds of No. 1110 shot, plus two quarts of butyl stearate and 100 cc. of oleic acid were added to a five quart assay laboratory jar, together with an assortment of pickled objects. This mill was closed and operated for twelve hours at room temperature. on opening it was found that the objects had received no copper coating or the lightest trace of copper discoloration.

' Example 7 A five quart laboratory assay jar was charged in exactly the same way as for Example 6 and run in an insulated cabinet at a temperature of 250 12 C. After six hours of running, the mill was opened and the objects within were found to be coated with a bright dense coating of copper .0005" thick.

In Example 6 the copper was run at a temperature below its recrystallization range and no plating occurred. In Example 7 it was run at a temperature within its range, and a substantial coating was laid down.

Example 8 300 pounds of iron shot No. 1110 were added to a mill 18" in diameter and 30" long, together with 50 pounds of finely divided zinc dust and seven gallons of high-flash naphtha and two quarts of oleic acid, plus seventy-five pounds of assorted metal objects which had been well pickled. The first objects which were removed from this mill had a coating of .0015" after ten hours of operation. Fresh objects were added to replace those removed. These were removed after a further period of ten hours when a third batch was added and it was found that after four or live batches had been removed that the weight of coating had'fallen to one ten-thousandth of an inch. In other words, little more than a flash coating was achieved.

Example 9 The mill described in Example 8 was loaded in exactly the same manner with the same charge and the same weight of objects, but was run at a temperature of 60 C. At this temperature the mill kept on plating and the weight of coating was not reduced even when the mill was kept in operation for twenty-eight days. Fresh additions of plating agent once a week were made along with small fresh additions of zinc dust.

It will be noted in Example 8 that the fatty acid did not continue to plate when run at room temperature, but that in Example 9 at a tem perature further into the recrystallization range of the zinc caused continuity of plating of the fatty acid.

The objects referred to in the examples above may be the washers mentioned or screws, bolts, nuts, nails, etc., or any other objects or articles regardless of size or shape.

} Example 10 A laboratory jar of five quart capacity was charged with three pounds of silver powder and twelve pounds of iron shot No. 1110. grams of oleic acid were added together with two quarts of high-flash naphtha and an assortment of small washers and other hardware which had been well pickled. The mill was rotated at room temperature for twelve hours. No plating of silver occurred.

Example 11 Three and one-half pounds of silver dust, twelve pounds of iron shot No.1110 were added to a five and one-half quart laboratory mill together with two quarts of butyl stearate and 100 grams of stearic acid. The mill was operated at 250 C. for five hours. Upon opening, the washers and other assorted objects were found to be covered with a dense silver coat 1.5 thousandths of an inch.

In the case of Example 10 the silver was below its recrystallization temperature and no plating occurred, whereas in Example 11 it was within the recrystallization temperature range and a thick coat of silver was deposited.

Exemplary A small five quart laboratory jar was charged with. three poundsof; zinc powder, twelve. pounds oflshotNo-.. 11.1.0, two quartsof butyl; stearate, 10.0. grams or stearic. acid. and an assortment. of. small. hardware. The. mill. was. closed. and, rotated for four. hours. at a. temperature of 125. C. Upon opening. the. objects were. found to. be. coated with 2.5; thousandthsv of. an. inch. of. zinc. The coating. obtained in this way was. very ductile. and. would stand verysubstantial deformation; in some cases sufiicient to rupture the steel base without injury to. the coating. Bhotomicrog-raphs were made. of the coating and they showed no diffusion oil the 'zinc. into the steel.

Example 13 A similar charge run under exactly identical conditions to Example 9 above was made except that" the temperature was maintained at 200 C. 'li'lie' adhesion ofthis coating was not as good as that: Example 12. Photomicrographs of the coating showed sporadic and barely perceptible indications of diffusion into the base metal.

Example 14 .Aoharge. similar to. Example 13 aboye,, but, run. at. 225 C.v was made. The. adhesion of this. coat? mg tothe, base; waspoor- The photomicrographs indicated a definite diiiusion of the zinc into. the. steel with fiormation of a definite alloy. layer which. is clearly visible...

From these last examples it. will. be. seen. that l Into a five quart. labora ory jar w s. h rge two pounds. of nails which had been well Pickled and washed, and ten pounds of coarse mesh zinc dust. to. serve. as. impacting, medium, cc... of water containing 2%. of platin chemicals composed of a three to one mixture, containing three partsot caprylic, acid to one part of a tertiary. amine highly solubilized with ethylene oxide. ,One qiuarter pound of dust. was added provide the. metal iorthe, coating. The, mill was closed and agitated for three hours. On opening the nails were found to be coated with a. bright. adherent coat of zinc of .002 in thickness. In this example the tertiary amine served as the cationic wetting agent referred to in the specificationof application No. 14,639.

Example 1 6 A five quart jar mill was charged as above, the organic amine being replaced by a tertiary amide. 0n opening the mill after three hours agitation, a bright adherent coating .002" was found to have been plated on the nails.

In this example the tertiary amide acted in a similar manner to the tertiary. amine of the previous example and filmed the zinc dust thereby protecting it from the action of the carrier liquid water.

and 1.2.00

Example. 1 7

Into a mill. 30' n d ameter and. one foot long was charged 5'50 pounds of coarse zinc, grit, fifteen pounds. of. fine. zinc dust. .50 p nds of Wel pickled. and washed; nail and e gallons of water. In the nine gallons of water was dissolved 70.0, of a mixture containing. three parts of a highly solubilized tertiary amide derived from a long chain unsaturated fatty acid, (and similar to the. one used in the preceding example) and one part or caproic acid. The mill was closed and agitated for three hours at twenty-five R. P. M; On opening the mill the nails were found to, be covered with a bright adherent coating of zinc approximately .00175 thick.

To summarize: r

This invention involves the joining of the metal surfaces oithe article and the particles by bringing, their surfaces into such actual physic metal to metal contact that atomic forces of attraction. cause, the surfaces to weld together by attachment f the particles to the articles and. to. eachothor.

his is accomplished by using v ry sm ll parholes of. etal for h coa ing and apply ng a force to distort each small particle individually a d. i t rfit. it nto p ace in the coatin he api on of; the. iorce necessary to d s ort an interflt. the particl s. may be achieved in various w ys. One pr ferr d. way is. to umble he article either lone or wi h cru hed ir n ho nail whiskers r th r su e ha d. ma r al. Other. ay .v su h, as by p jecting the m a oatin particles Suspended in a liquid vehicle containing the plating: romo ers a he r cles to be coated by means of. an i p ll r or ee ha been successfully used- Any other system capabl of ndi i al y distortins the sma l. etal p r c e nd eld a d interfitt-ins t em. into a e o the surfaces of.

he. ar cles. to. be coa ed and to each. ther could be successfully used without departing from the scope r p po e of t s invention...

It ha be n s wn t at two d r of pl in are. nvo ved n me n a p ess of metal cladding the surfaces of metals, using finely divided. metal dusts to provide the coating metal. These are the adhesive coatings laid down into thev microscopic roughnesses of the base surfaces and. th co es ve bond er other p t cl s ar superimposed on the initially deposited layers.

It. has been sh n that e p or t ha no een. able to achieve any coa in her t an a smear type o adhe i e coa in ereas is dislos re sho s. means f r uild n p d r coatin oi. any d rcdthickn ss.

It has been shown further that this is accomplishcd. in a very surpr sing r. na ely by lmi g the. surfac s of. the ar icles d particle with. a. thin oily him. which lm. i pr fe ably capa lc of ex rtin a so ent ac ion on. metal oxides to assist the mechanical forces in securlog, cl an metal surfac s n a dition o its pr perty of filming metals. Where the film former does not have any solvent or oxide removal properties of its own, it can be fortified by additions which do have such action, such as weak acids like some of the organic acids-such as citric, tartaric, oxalic, or weak alkalis, such as dilute solutions of ammonia.

In the various illustrative examples and in the specification, various oily film-forming materials such as the fatty acids, reaction products of fatty acids with nitrogen, cellulose gum, etc. have been spirit of this invention which teaches that an oily material is useful in promoting the joining of metal surfaces. This is entirely new and novel.

Similarly, in the examples and specification, various acids and alkalis such as citric, caprylic, acetic, and weak ammonia have been disclosed for use in facilitating the removal of oxide and other films from the surfaces of the metals to be joined. It is obvious that other weak organic acids having similar properties may be substituted with more or less efficiency for these mentioned without departing from the spirit of this invention.

7 I claim:

1. A method of cladding metal articles with a metal selected from the group consisting of tin, lead, cadmium, zinc, aluminum, magnesium, copper, silver, gold and alloys thereof, which method comprises mixing said articles with pieces of im pacting material in a liquid carrier containing particles of said selected metal in amount sufficient to provide a desired thickness of cladding metal on said articles and in proportion ranging from /130 to of the combined weight of said articles and impacting material, said carrier liquid being in amount between .143 and 100 of the weight of the metal dust particles and including dispersed therein an organic surface-active, film-forming compound unreactive with said carrier liquid and selected from the group consisting of the fatty acids of 6 to 22 carbon atoms and the amines and amides of said acids, said compounds being present in amount in the range of the order of .7 to .001 of the carrier liquid by weight and at least sufficient to substantially cover said articles and to enclose and protect the powder particle surfaces with molecularly thin films, forcibly impacting and rubbing said filincoated dust particles in admixture in said carrier liquid onto the surfaces of said articles to flatten said particles and rupture said films and bring the particles in metal to metal contact with the said surfaces and with each other, the temperature of the treating carrier liquid being at least equal to the minimum temperature of recrystallization of the said metal particles to clad said surfaces with adherent surface layers of said flattened particles with entrapment of residual inclusions of said film-forming compound retained in random distribution among said fiattened particles of said cladding layer, and continuing said impacting and rubbing of said filmcoated particles onto said adherent surface layers to build up said surface layers to desired thickness on said articles.

2. A method of mechanically cladding metal articles as set forth in claim 1 in which the carrier liquid is a non-aqueous organic compound which is a liquid solvent for the film-forming material.

- 3. A method of mechanically cladding metal 16 articles as set forth in claim 1 in which the carrier liquid is aqueous and holds the film-forming material in solution therein. 4. A method of mechanically cladding metal articles as set forth in claim 1 in which the carrier liquid is aqueous and contains the film-forming material dispersed as an emulsion therein.

5. A method of mechanically cladding metal articles as set forth in claim 1 in which the carrier liquid is aqueous and includes the film-forming material and a weak water-soluble organic carboxylic acid acting to dissolve oxides from the surface of the metal particles, said material and said acid constituting together .7 to .001 of the carrier liquid by weight.

6. A method of mechanicaly cladding metal articles as set forth in claim 1 in which the filmforming material is an aqueous solution of a tertiary amide of one of the said fattyacids.

7. A method of mechanically cladding metal articles as set forth in claim 1 in which the carrier liquid includes the film-forming compound and an organic acid selected from the group consisting of tartaric, citric, caproic, and caprylic and acetic acids constituting together with the film-- forming material .7 to .001 of the carrier liquid by weight.

8. A method of mechanically cladding metal articles as set forth in claim 1 in which the carrier liquid is water and includes the film-forming compound and a weak alkali to effect the dissolving of the oxides from the surfaces of the metal particles, the film-forming compound and Weak alkali together constituting .7 to .001 of the carrier liquid by weight.

9. A method of mechanically cladding metal articles as set forth in claim 1 in which the carrier liquid is water and includes the film-forming compound and ammonia to effect the dissolving of the oxides from the surfaces of the metal particles, the film-forming compound and ammonia together constituting .7 to .001 of the carrier'liquid by Weight.

10. A method of cladding metal articles as set forth in claim 1 in which the film-forming material is an aqueous solution of a tertiary amine of one of the said fatty acids.

11. A method of cladding metal articles as set forth in claim 1 in which the coating metal particles are copper.

12. A method of cladding metal articles as set forth in claim 1 in which the coating metal particles are silver.

ERITI-I T. CLAYTON.

Name Date Mixon May 8, 1945 FOREIGN PATENTS Country Number Number Date Great Britain Mar. 21, 1941 

1. A METHOD OF CLADDING METAL ARTICLES WITH A METAL SELECTED FROM THE GROUP CONSISTING OF TIN, LEAD, CADMIUM, ZINC, ALUMINUM, MAGNESIUM, COPPER, SILVER, GOLD AND ALLOYS THEREOF, WHICH METHOD COMPRISES MIXING SAID ARTICLES WITH PIECES OF IMPACTING MATERIAL IN A LIQUID CARRIER CONTAINING PARTICLES OF SAID SELECTED METAL IN AMOUNT SUFFICIENT TO PROVIDE A DESIRED THICKNESS OF CLADDING METAL ON SAID ARTICLES AND IN PROPORTION RANGING FROM 1/480 TO 4/3 OF THE COMBINED WEIGHT OF SAID ARTICLES AND IMPACTING MATERIAL, SAID CARRIER LIQUID BEING IN AMOUNT BETWEEN .143 AND 100 OF THE WEIGHT OF THE METAL DUST PARTICLES AND INCLUDING DISPERSED THEREIN AN ORGANIC SURFACE-ACTIVE, FILM-FORMING COMPOUND UNREACTIVE WITH SAID CARRIER LIQUID AND SELECTED FROM THE GROUP CONSISTING OF THE FATTY ACIDS OF 6 TO 22 CARBON ATOMS AND THE AMINES AND AMIDES OF SAID ACIDS, SAID COMPOUNDS BEING PRESENT IN AMOUNT IN THE RANGE OF THE ORDER OF .7 TO .001 OF THE CARRIER LIQUID BY WEIGHT AND AT LEAST SUFFICIENT TO SUBSTANTIALLY COVER SAID ARTICLES AND TO ENCLOSE AND PROTECT THE POWDER PARTICLE SURFACES WITH MOLECULARLY THIN FILMS, FORCIBLY IMPACTING AND RUBBING SAID FILMCOATED DUST PARTICLES IN ADMIXTURE IN SAID CARRIER LIQUID ONTO THE SURFACES OF SAID ARTICLES TO FLATTEN SAID PARTICLES AND RUPTURE SAID FILMS AND BRING THE PARTICLES IN METAL TO METAL CONTACT WITH THE SAID SURFACES AND WITH EACH OTHER, THE TEMPERATURE OF THE TREATING CARRIER LIQUID BEING AT LEAST EQUAL TO THE MINIMUM TEMPERATURE OF RECRYSTALLIZATION OF THE SAID METAL PARTICLES TO CLAD SAID SURFACES WITH ADHERENT SURFACE LAYERS OF SAID FLATTENED PARTICLES WITH ENTRAPMENT OF RESIDUAL INCLUSIONS OF SAID FILM-FORMING COMPOUND RETAINED IN RANDOM DISTRIBUTION AMONG SAID FLATTENED PARTICLES OF SAID CLADDING LAYER, AND CONTINUING SAID IMPACTING AND RUBBING OF SAID FILMCOATED PARTICLES ONTO SAID ADHERENT SURFACE LAYERS TO BUILD UP SAID SURFACE LAYERS TO DESIRED THICKNESS ON SAID ARTICLES. 